1. Technical Field
The present invention generally relates to liquid ejection heads that eject droplets from nozzles and methods of manufacturing the liquid ejection heads. In particular, the invention relates to an ink jet recording head that ejects ink droplets and a method of manufacturing the ink jet recording head.
2. Related Art
An ink jet recording head that ejects ink droplets is a representative example of a liquid ejection head that ejects droplets. One example of the ink jet recording head includes a nozzle plate with nozzles perforated therein, a flow channel-forming substrate in which a plurality of pressure-generating chambers communicated with the nozzles are formed, a piezoelectric element serving as a pressure-generating unit and being disposed at one side of the flow channel-forming substrate, and a reservoir-forming substrate (protective substrate) having a reservoir portion communicated with the plurality of pressure-generating chambers and being joined onto the flow channel-forming substrate (e.g., refer to Japanese Unexamined Patent Application Publication No. 2007-98813).
The flow channel-forming substrate of such an ink jet recording head is, for example, formed of a silicon single crystal substrate having a (110) plane orientation, and the pressure-generating chambers (ink flow channel) are formed by anisotropically etching the silicon single crystal substrate. To be more specific, the pressure-generating chambers are formed by anisotropically etching a silicon single crystal substrate such that side surfaces extending in the longitudinal direction are composed of a first (111) plane perpendicular to a (110) plane and that side surfaces extending in the width direction (transversal direction) are composed of a second (111) plane intersecting the first (111) plane.
In the case where a flow channel-forming substrate is formed of a silicon single crystal substrate having a (110) plane orientation, a reservoir-forming substrate is usually also formed of a silicon single crystal substrate having a (110) plane orientation. Since the reservoir portion is formed to align with the pressure-generating chambers, side surfaces of the reservoir portion that extend in the width direction (the longitudinal direction of the pressure-generating chambers) are composed of a first (111) plane and side surfaces that extend in the longitudinal direction are composed of a plane including a second (111) plane.
This means that the flow channel-forming substrate is joined onto the reservoir-forming substrate while having the first (111) planes of both substrates oriented in the same direction.
A (110) silicon single crystal substrate used as a flow channel-forming substrate or a reservoir-forming substrate is susceptible to cracking along the first (111) plane. If the first (111) plane of the flow channel-forming substrate is oriented in the same direction as the first (111) plane of the reservoir-forming substrate, cracks may occur along the first (111) planes even when the flow channel-forming substrate and the reservoir-forming substrate are joined together.
In general, in forming the flow channel-forming substrate or the reservoir-forming substrate, a silicon wafer in which a plurality of flow channel-forming substrates or reservoir-forming substrates are collectively formed is prepared and diced along a break pattern. The break pattern is constituted by, for example, a plurality of through holes that form dicing lines and fragile portions between the holes (e.g., refer to Japanese Unexamined Patent Application Publication Nos. 2006-218716 and 2002-313754).
The through holes constituting the break pattern are usually formed by anisotropically etching the silicon wafer, as with formation of the pressure-generating chambers. Thus, through holes can rarely be formed into a straight line along the dicing line in a direction intersecting the first or second (111) plane. The width of the break pattern thereby becomes relatively large. If the width of the break pattern is large, the number of flow channel-forming substrates or the reservoir-forming substrates that can be formed on one silicon wafer decreases, resulting in an increase in cost. The width of the break pattern is preferably as small as possible.
In forming a flow channel-forming substrate having pressure-generating chambers or a reservoir-forming substrate having a reservoir portion as described above, a break pattern is formed in a direction along the first (111) plane and in a direction orthogonal to this direction. The break pattern extending in such directions can be formed to have a relatively small width. Accordingly, the flow channel-forming substrate has been joined with the reservoir-forming substrate so that their first (111) planes are oriented in the same direction. In other words, the reservoir portion of the reservoir-forming substrate has side surfaces that extend in the width direction (the longitudinal direction of the pressure-generating chambers) and are composed of the first (111) plane, and side surfaces that extend in the longitudinal direction and are composed of planes including a second (111) plane.
As described in Japanese Unexamined Patent Application Publication No. 2007-98813, in forming such a reservoir portion by anisotropic etching, a correction pattern having a particular shape is provided in side surface portions extending in the longitudinal direction of the reservoir portion so that the side surfaces in the longitudinal direction of the reservoir portion are formed into a straight line. However, the shape of the side surfaces of the reservoir portion is difficult to accurately control through the correction pattern. Moreover, since regions for forming the correction patterns are needed, the number of substrates that can be produced from one wafer decreases.
It should be noted that the problem of substrates' susceptibility to cracking is not unique to ink jet recording heads that eject ink droplets but is present in other types of liquid ejection heads that eject droplets other than ink droplets.